Seasonal Affective Disorder (SAD) is a seasonal pattern of clinical depression that also correlates with changes in appetite, weight regulation, hormone profiles, and social interactions. This suite of correlated traits (except for the depression) is characteristic of many birds that show dramatic seasonal shifts in energy regulation and social structure as an adaptive anticipatory response or an adaptive reactive response to seasonal environmental changes. Thus, birds may be excellent models for understanding basic physiological processes that are associated with seasonal affective disorders in humans. However, while we understand many of the component parts of these seasonal cycles, we know relatively little about the adaptive significance of the joint regulation of these cycles. To this end, we propose an experiment designed to evaluate the correlated changes in spatial memory, neuroanatomy, hormone profiles, energy regulation patterns and activity budgets in adult Carolina chickadees maintained under natural photoperiods. Carolina chickadees will be used in this study because these birds store food in hundreds to thousands of distinct sites; retrieval of this food is partly dependent on spatial memory. Thus seasonal variation in energy storage patterns should be correlated with seasonal variation in hippocampal formation (HF) and spatial memory capacity. The project includes a yearlong study where adult birds are housed under laboratory conditions with natural photoperiods but constant temperature. Caching rates and body mass will be monitored under constant rates of food access for a 32-day period, then the birds will be given a set of spatial memory tests in which they are allowed to search a room for previously stored seeds. These data will provide a direct comparison between energy regulation tactics and spatial memory capacity. Movement patterns and general time budgets will be generated from focal-animal behavioral samples. After the behavioral tests are completed, we will test for correlated changes in size and cytogenesis in the HF. Cytogenesis will be measured using BrdU injections administered during the spatial memory trials; HF size will be measured on each bird at the end of each experiment. Hormone profiles will be measured from fecal samples taken at dawn and dusk throughout the experiment. Seasonal cycles of depression often correlate with seasonal cycles in a variety of physiological traits. Only an integrative approach will tell us how these cycles relate to on another. An understanding of the adaptive significance of the suite of traits that cycle annually in natural systems will give us a unique insight into this important component of these seasonal disorders.